One of the major problems encountered in the waterflooding of permeability-stratified reservoirs is the preferential flow of water through the more permeable zones between injector and producer wells. This preferential flow greatly reduces the sweep efficiency of driving fluids. This reduction in sweep efficiency can also occur in steam and miscible CO.sub.2 -flooding processes.
To improve sweep efficiency, the permeability of such zones must be reduced. This technique is commonly known as permeability control. Polymer gels are often placed into high permeability zones to impede the flow rate through such zones.
Metal-complexed polymer gels are widely used for profile control. For example, Al(III) and Cr(III) are used to crosslink polyacrylamide. Other metal ions, such as Ti(IV), Zr(IV), Fe(III), etc., are also useful as gelants for polymers.
Several limitations may interfere with the use of metal ions in the 1 preparation of gels for profile control. One limitation is that each metal is reactive only to certain functionalities. For example, Al, Cr, and Zr are reactive to amide and carboxyl groups, while Ti is reactive to hydroxyl groups. A proper match of the polymer with the appropriate metal crosslinker must be considered. There is no presently known general metal crosslinker for all polymer types. Carbonate, bicarbonate, and sulfate anions are known to interfere with the gelation of Cr, Zr, and Al. Another limitation is that pH control is important for most metal crosslinking reactions. It is easy to control the pH when the gel is prepared above surface but difficult to do when an in-situ gelation process is ued. Furthermore, ligand metal bond formation and stability may be affected by high ionic strength and the temperature of reservoir brine. At substantially high brine concentrations and high temperatures, metal-ligand bonds can dissociate due to unfavorable equilibria.
Therefore, what is needed are economical amino resins which will co-gel and crosslink covalently with all polymers known to be useful for profile control where said polymers contain amine, amide, hydroxyl, or thiol functionalities. The utilized gelation reaction should proceed under all pH conditions; should not require an acid or base to catalyze; and should not be affected by reservoir brine. The resultant linkages should be stable at substantially high temperatures and high salinities.